This invention relates generally to oscillators and more particularly pertains to an oscillator having controls associated therewith for randomly varying the frequency of the oscillator output signal.
Communication equipments frequently have circuits for tracking the phase or frequency of a signal. An example of such a circuit is a phase locked loop. Such circuits are ordinarily designed to be capable of tracking the signal within specified limits of noisy variation of the signal's phase or frequency. In testing to determine whether the actual tracking capability of a particular embodiment of such a circuit meets design criteria, it is useful to employ an oscillatory signal source in which the signal frequency is randomly varied by a process having known and controllable characteristics.
If a process used to randomly vary the frequency of an oscillator output signal were capable of being faithfully reconstructed, the reconstructed process could be generated and used at a remote signal receiver to remove the noise from the received signal. In such a case, the application of the noise-like variation to the frequency of an oscillator output signal in a controlled manner amounts to scrambling the signal while the subsequent removal of the noise constitutes unscrambling the signal. An example of the use of such a process would be the encoding of pay TV signals such that the reception of such signals would not only reouire a viewer to obtain the necessary decoding circuitry but would also require a valid code for decoding the picture. Without the code, non-subscribers could not unscramble the picture even though they have built or obtained the necessary decoding box through means other than the pay TV company.